On large farms many crops are cultivated and harvested by machines which process several rows at a time. These machines are designed to operate on the assumption that all of the rows are substantially evenly spaced. The machines which make the furrows prior to planting, make a plurality of nearly perfectly evenly spaced rows for each pass across the field. In practice, however, it is impossible to maintain the exact row spacing between successive passes of the machine across the field. The first row next to the last row of the previous pass of the machine thus has become known as the "guess" row because it has been impossible for even the most skilled tractor operator to maintain the exact spacing. Thus, when the operator does not keep the spacing exactly the same between the adjacent rows of successive passes of the furrowing and planting machines, the harvesting machine will either miss an entire row or depending upon the crop and the harvesting mechanism, it will either destroy or improperly harvest at least one and sometimes more rows of the particular crop. Since many harvesting machines are automatically steered by mechanisms which have sensors which contact the crop, as for example, Schmidt, U.S. Pat. No. 3,326,319, an inattentive operator can and often does destroy a great quantity of crops because the machine does not take into consideration the uneven row spacing in the "guess row".
The problem of spacing crop rows is discussed in Hunsicker, U.S. Pat. No. 2,827,704 granted Mar. 25, 1958 and the patent teaches a visual sighting mechanism attached to the tractor.
Bakehouse, U.S. Pat. No. 3,028,678 granted Apr. 10, 1962 also is concerned with spacing and uses a cross bar attached to the tractor with chains reaching to the ground to assist the operator in visually sighting the previous row.
The first automatic furrow following device for a wheeled tractor found by Applicant in the prior art is Blachet, U.S. Pat. No. 3,548,966 granted Dec. 22, 1970. Blachet discloses a single wheel device mounted on the front end of a wheeled tractor.
There are many sophisticated devices in the prior art for following a guide wire such as Amos, U.S. Pat. No. 3,258,082 granted June 28, 1966, see also Ruoff, U.S. Pat. No. 4,131,176 granted Dec. 26, 1978 in which a sensor moves the wheel of the vehicle in relation to a fixed guide rail.
A very sophisticated guidance system is shown in Hobday, U.S. Pat. No. 3,679,019 granted July 25, 1972 in which a wheeled vehicle follows a buried wire.
All of the previously cited references relate to wheeled tractors and vehicles. Crawler type vehicles are also automatically steered but all of those found by Applicant follow a guide-wire. The earliest track laying, guide-wire following machine found by Applicant is Flom, U.S. Pat. No. 3,181,441 granted May 4, 1965. The latest track laying guide-wire following apparatus found by Applicant is Dale, U.S. Pat. No. 3,905,715 granted Sept. 16, 1975.
A furrow following wheeled plow is shown in Sieling, U.S. Pat. No. 3,123,148 granted Mar. 3, 1964. This device is designed to straighten out successive furrows even though the straightening process would change the spacing between adjacent furrows. The Sieling plow cuts only a single furrow with each pass across a field.
A furrow following device is shown in Burvee, U.S. Pat. No. 3,765,501 granted Oct. 16, 1973. Burvee discloses a device for a wheeled tractor and connects the furrow following device to the mid-point of the frame of the tractor. The furrow following device has only a single point of contact with the furrow; mainly a cone wheel spaced from the front wheel of the tractor.
A commercial furrow following device for wheeled tractors is made by electronics system division of Geosourse, Inc. of Modesto, Calif. and is sold under the trademark TAG. In this system, the furrow following device is mounted directly to the front portion of the frame of the wheeled tractor.
The prior art system for making furrows with crawler tractors is as follows: For the initial pass, a transit is set up and stakes or bags are placed along the line for the tractor operator to follow. A device for making a "guide furrow" is attached to the rear cross bar and this becomes the guide for the operator on the second pass. When the operator has completed the first pass and has turned his crawler tractor to make the second pass, the tractor operator aligns a marking device on the front of the tractor such as the radiator cap with the previously made marking furrow and then sights along these two marks down the entire length of the field to a distant arbitrary mark such as a tree. The operator then steers the tractor toward the distant point and attempts to keep his eye on the distant point and the radiator cap or other marker on the tractor during the entire furrowing pass. A problem with this procedure is the operator can not keep his eye on the machinery to see whether or not the fertilizer, fungicide and other chemicals are being injected into the soil. Primarily, however, driver fatigue, dust, and glaring sun make it very difficult for drivers, using the present system to maintain the critical row spacing hour after hour.
None of the prior art systems for causing a wheeled tractor to move parallel to a previously formed furrow are adaptable for track laying tractors. The reason for this is the fact that a wheeled vehicle with steerable front wheels moves in an arc when the front wheels are steered to the right or left. In contrast, a track laying vehicle pivots when it is steered. To add to this complication, the tractor does not pivot about a single point but in fact pivots about two different points. If the tractor is steered to the right, the pivot point lies beneath a center point on the right track laying mechanism. If the tractor is steered to the left, the pivot point lies beneath the left track laying mechanism. Further, the pivot point is not always at the same point beneath the track laying mechanism. L. L. Karafiath in his book SOIL MECHANICS FOR OFF-ROAD VEHICLE ENGINEERING, TRANS TECH PUBLICATIONS, T.L., 235, point 6, k, 34, E.N.G.I. (1978 ) at Page 443 and FIG. 399, demonstrated that the stresses under the track are trapezoidal at zero draw bar pull. As the draw bar pull gradually changes, the distribution of stress changes to an approximate triangle with the acute angle at the rear driving sprocket. Thus, it may be concluded, that the pivot point under full draw bar load is approximately at the center of the tread at the rear sprocket. These pivot points are shown in FIG. 7 of the drawings as P.sub.1 under the left track and P.sub.2 under the right track.